Telephone system.



T. H. FERGUSON.

TELEPHONE SYSTEM.

APPLlcATloN FILED 11116.15. 1912.

Patented July 31, 1917.

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T. H. FERGUSON.

TELEPHONE SYSTEM.

APPLICATION FILED AuG.15. |912.

Patented July 31, 1917.

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TELEPHONE SYSTEM. APPLICATION msn Aue.15. |912'.

Patented July 31, 1917.

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T. H. FERGUSON.

TELEPHONE SYSTEM.

APPLICATION FILED AUG-15,1912.

, l ,235,302. Patented July 31, 1917.

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T. HIERGUSCN.

TELEPHONE SYSTEM.

APPLlcATloN FILED Autms. |912.

Patented July 31, 1917.

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T, H. FERGUSON. TELEPHONE SYSTEM.

APPLICATION FILED AUG-l5. i912. 1,235,302. f

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JUIN!" Z0 Q) MNHN Patented July 31, 1917.

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THOMAS H. FERGUSON, OF OAK PARK, ILLINOIS, ASSIGNOR 'IO KELLOGG SWI'IGI-IBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, .A CORPORATION 0F ILLINOIS.

TELEPHONE SYSTEM.

Application filed August 15, 1912.

'o ZZ 'w 7mm t may concern Be it known that I, THOMAS I-I. FERGU- soN, a citizen of the United States, residing in Oak Park, county of Cook, and State of Illinois, have invented new and useful Improvements in Telephone Systems, of which the following is a specification.

The present invention relates to automatic telephone systems generally, and more particularly to that class in which a number ot' lines extend to one location, such as a private branch board, and are severally called by transmitting impulses corresponding to a single number.

Heretoore it has been the practice, where a number of lines have run to a private branch board, (l) to give each line a separate number so that it may be called just as any other number, or (2) to assign one number to the several lines and to provide a socalled selector connector7 which, when stepped to the contacts of the first of said lines, would automatically step into engagement with the contacts of the second line if the first be found to be busy, and would continue its advance until it found an idle one or' said lines; or it all of said lines were busy, it would step to an eXtra set of contacts, from which a busy back signal would be transmitted to the calling. party. The latter arrangement, although a decided advance over the former, because of the saving of time in obtaining connection with the branch board, nevertheless requires a large number of dead, or extra, contacts on its connectors which, on the average, would approximate anywhere from twenty to forty per cent. of the total number of contacts.

The object of the present invention is to avoid the necessity of using these eXtra busy back contacts and to transmit the busy back signal from the last line ot the group running to the branch board in case it is also found busy. By this arrangement, the socalled eXtra contacts may be utilized as the terminals of other lines, andthe connectors thus given their full quota of connections.

Another object of the invention is to bring about this economy ot contacts without increasing the number of relays or other substantial parts of prior systems to which the invention is applicable.

Specification of Letters Patent.

Patented July 31, 1917.

Serial No. 715,170.

In carrying out my invention, I associate, with the testing wiper of the selector connector, apparatus which will (l) apply ringing current, (2) step the connector ahead one step, and transmit a busy back signal to the calling party, in exact accordance with three different electrical conditions of the test contact of the line tested. Thus, in the embodiment herein disclosed, ringing current will be transmitted over the calling line when the test contact of the line is connected to battery; the connector will be stepped ahead if the contact tested is connected to ground; and a busy back signal will be transmitted if the contact tested is open, that is, disconnected from other parts.

From this outline, it will be apparent that f my invention is of broad scope, and although disclosed in connection with a specitic type of electrical apparatus, is not necessarily limited thereto, but is capable of broader' application.

In applying my invention to a telephone system, I have selected a full automatic system of the class in which the well known selectors and connectors of the two-dimension type are employed in conjunction with similarly constructed line selectors controlled by master-switches. In such systems, the movable contacts or wipers of the two-dimensiony switch are associated with a large number of fixed, or passive, contacts ar-` ranged in a bank, and the wipers are rst given a movement in one direction and then a movement at an angle thereto, the former, or primary, movement bringing the wipers to a desired group of bank contacts, and the latter, or secondary, movement causing the wipers to engage the desired bank contacts in the selected group. On a basis of a ten thousand line exchange, provided with hundred point switches and ten per cent. trunking, there would be one hundred master-switches, one thousand line selectors, one thousand first selectors, one thousand second selectors, and one thousand connectors; each subscribers line would be multipled to ten line selectors and ten connectors; the line selectors and first selectors would be united in pair without multipling; the wipers of the second selectors would be multipled to the bank contacts of one hundred rst selecselectors; and the wipers ot each connector would be inultipled to the bank contacts of one hundred second selectors.

With the above outline, the invention will be best understood by referring to the accompanying drawing and the following detailed description.

In said drawing, Figure l, including Parts l, 2 and 3, illustrates the preferred embodiment of the present invention applied to an autoniatic system ot the class mentioned; Fig. 2 is a modified connector circuit adapted to be used in the circuit of Fig. l instead ot the connector circuit illustrated in ldart 3 ot that ligure, Figs, 3, l, and 5 are elevations ot' a line selector Viewed troni different sides, the switch beingl also typical ot the other selectors and connectors einployed in the systein; Fig. 6 is a plan *new ot said switch; Fig. `i' is a sectional plan ot a portion ot the saine, taken on a plane indicated by the line 7-7 of e; Fig. 8 is a detail vView ot certain ot the connector off-normal contacts;I and Figs. 9 and Fig. l0 are top and side elevations, respectively, ot a master-switch employed in the control ot the line selectors, Throughout these views, like characters refer to like parts.

Before proceeding `with a detailed description ot the circuits and apparatus ot the systein to which niy invention is applied, it may be pointed out that the changes over prior systems ot the art, in order to embody the present invention, are liniited to (l) changes in the line circuit, and (2) changes in the connector circuit, For a tull iuiderstanding of the invention, however, it will be necessary to explain the remaining circuits oit the system, and this will be done in the regular order.

Apparatus.

ln Fig. l, M at the lett ot the diagrani designates a subscribers station, united to the inain exchange by the line linibs lii, which terminate in the inultiple contacts ot line selectors and connectors. At the opposite end of the diagram, N designates a siinilar subscribei"s station which is united by line linibs P', S to the exchange, and the line liinhs are similarly connected to the multiple contacts ot line selectors and connectors, Connection is obtained between the line at the lett and the line at the right through the agency of a inastcnswitch O, a line selector @,f a lirst selector U, a second selector V, and a connector, or selector connector, W. Upon the prei'iously noted basis of a ten thousand line exchange einploying hundred point switches and ten per cent. trunking, there would be one hundred master-switches G and one thousand oit each of the switches Q, V and TV. lpon this saine basis, the subscribers? lines would be divided into groups of one hundred, and ten line selectors would be assigned to each group, thus enabling each line to be niultipled to corresponding bank contacts on ten dili'ereiit line selectors. Each group of line selectors would be under the control ot one master-switch haring a pair of bank contants assigned to each line selector, Each subscribers line, or each line of a group ot lines running to one subscriber, would also be inultipled to the corresponding bank contacts ot ten connectors. ln the diagram, only two ot the ten sets of niultiple contacts ot the line selectors and connectors lare illustrated, while but live pairs ot bank contacts of the inasterswitch are shown. he niorable contacts, or wipers, ot each line selector are tied to the cor qesponding wipers of a iirst selector U, thus providing one thousand direct connections between the one thousand line selectors and the one thousand iirst selectors. rihe wipers ot the second selectors are niultiply connected to the bank contacts ot the lirst selectors, and since there are one thousand ot each ot these sw'tches, the wipers of each second selector are connected to the corresponding` contacts of one hundred first selectors. Similarly, the wipers ot' each ot the one thousand connectors are connected to the corresponding` contacts ot one huncrcd second selectors.

ln operating the parts to establish connecn tion between stations lvl and hl, the calling party at station i'l renioies his receiver troni its hook and thereby through the agenct7 ot the master-switch 0, sets an idle line selector Q in operation to automatically seek out and establish connection withk his line, thus ei:- tending the calling line circuit to the vfirst selector U, paired with the actuated line selector Q. The calling party then, `by ineans of his calling inechanisin. transmits h nuinber of impulses, corresponding to the digits of the nuinber ot the siibscriber wanted, and this niethod will be pursued eren though the wanted subscriber hare a nuniber or" lines running to his station, rhe first series of these iinpulses operates the connectedtirst selector U so as to cause it to pick out an idle second selector V. associated with the thousand group to which the called line belongs. Thus, it the inunber ot'rthe calling party were QSO() soine odd, rthe iirst set of inipnlses would nieve the wipers of the selector to the second group ot its bank contacts, and these wi iers uwould then automatically nieve over the contacts in this group until an 'idle contact was encountered, thereby extending the circuit of the calling party to an idle second selector in the second thousand group. llhe second series ot irnpulses would siinilarly operate the second selector V to pick out and establish connection with a connector associated with the hundreds group to which the called station belongs. rlhus it three impulses were transmitted over the circuit, the second selector Y would move its Wipers to the third group ot its bank contacts, and the Wipers Would then automatically move over the contacts in that group until an idle one Was selected, thereby extending the circuit of the calling line to a connector having access to the called station. The third series of impulses would cause the connector to move its Wipers to that group of ten contacts in which the contacts of vthe called line or lines were included, andthe final series of impulses would cause the Wiper to move over the contacts in this group until the contacts corresponding to the first line ruiming to the called station Were encountered. it this line Were found to be busy, the connector would step into engagenent with the contacts ot the next line running to the same substation, and so on automatically until the last line rrmning to the same station was encountered; and then, it this were busy, a busy back signal .vould be transmitted to the calling party. However, if any of the lines running to the called station were idle, the connection vfould be completed and the called party signaled.

Each line is provided at the exchange with,

a line relay LR, which is instrumental in closing a circuit through the master-switch 0 upon the initiation of a call, and a cut-o relay CO, which is used to destroy the normal substation control of the line relay and to otherwise vary the line connections. circuit opening relay CK is also provided for interrupting' the normal connection to spring 8l Whenever the line is a calling line.

The master-switch O comprises a pair ol' wipers 20, 21, cooperating With bank contacts 22, MM, the complete operation being controlled by the relays 2l, 25, as hereinafter more 'fully pointed out.

The line selector includes the wipers 26, 2T, 2S and 29, cooperating with bank .contacts 30, 3l, 33. lWipers 26, 27 and 28 partake ot the tivo movements or' the switch, that is, the primary and secondary movements, While Wiper 29 partakes only of the primary movement. rllhis primary movement is brought about by primary magnet PM, controlled by primary relay PR, While the secondary movement' is similarly brought about by secondary magnet SM controlled by secondary rela-y Slt. rhe release of the svvitch, which permits its return to normal position, is brought about by release magnet RM, controlled by release relay RR. The switch is also provided with primary and secondary oit-normal contacts iD() and SO, which are operated respectively upon the first primary and the first secondary movements of thc switch. Although each subscribers line is multiply connected to ten line selectors and ten connectors, two such multiple connecand actuated by a motor magnet tions only are shown in the drawing, Wherein bank contacts 30,13l 32, 33', and cooperating Wipers 26', 27', 2S and 29 belong to a second line selector, and contacts 3G, 36', 3T, 37', 3S and 3S are bank contacts of two connectors.

The first selector U includes the Wipers 3Q, 40 and ell, which cooperate With bank contacts 42, 4:3 and et, also multipled, in responseto the operation or the primary mag-V net PM', controlled by the primary relay Pl, and the secondary magnet SM, controlled by the secondary relays SR and SR. The Wipers in this case all partake of the primary and secondary movements, and the switch is released through the operation of the release magnet RM and the `release relay RR. The primary off-normal contacts PO, and the secondary ott-normal contacts SO, here, as before, are operated upon the first primary and secondary movements of the Wipers, respectively. The circuit associated with this selector also includes a reversing relay RV for reversing the direction of current applied to the calling line, and an associated relay e5, all of Which will be more fully understood from the subsequent description.

The second selector V comprises Wipers a6, a7, 48, which cooperate with bank contacts 49, 50, 5l, in the same manner as first selector U. In this case, the corresponding relays, magnets and ott-normal contacts are designated by the corresponding reference characters having the exponent 2 instead of the prime.

The connector EV is provided with Wipers 52, 53, 5a, cooperating with the bank conams 55, 5c, 57, 55a, 56a, 57a, 55h, 56D, er, and in this instance, as before, they partake of both primary and secondary movements in response to the primary magnet PMS and the secondary magnet SMS respectively, and return to normal upon the operation of the release relay RRS and release magnet RM. ln this inst-ance, the primary od-normal switch contacts are designated P03, and the secondary ott-normal Vcontacts S03. In addition to these parts, the circuit is provided with a busy relay'BR, a ringing relay RG, an auxiliary ringing relay RG', a control relay R, a tip relay TB, a flip-nop relay FF, and a closing relay CR, all of Which cooperate in the manner hereinafter more fully set forth.

The equipment at each substation includes the usual switch-hook Git, receiver 65, callbell (5G, transmitter 67, condenser 67, and

ycalling mechanism 68.

The line circuit at the right of Fig. l is the same as that at the left and is provided with a line relay LR, cut-ott relay CO, and circuit closing relay CK, The line circuit here shown in Jfull is associated with the connector contacts 55a, 562' and 57a. It may be assumed tor the purpose of description that both the line associated with contacts 55, 5G, 57, and the line associated With contacts 55, 56h, 57h, run to thesame station as the line associated with contacts 55a, 5G, 571. ln other Words, for the purposes of this description, it may be assumed that three lines run to substation lil. Under this assumption, as Will hereinafter more fully appear, the niet tivo lines have the same connections, While the third line has its connections slightly modified.

Operation.

lilith this description of the. character of the apparatus diagrammatically illustrated in Fig. l, 'it-is believed that a description or the operation will most clearly bring out the functions olf the apparatus and the nature of the invention of the present application.

Assuming that a party at substation M desires to converse With a party at substation N, and assuming that the number of the lattei-s telephone issl, and, as before indicated, that three lines, associated with the contacts illustrated at the right of the diagram, run to substation N Vand are to be reached by calling the same number, namely, 3456; then the calling party rst removes his receiver '65 and thereby establishes a circuit which may bey traced from the live, or negative, pole of the battery B, through resistance ).71, closed contact 7G of the cut-ofiP relay CO, line limb il, closed contact 75, the Winding of the loch controlling magnet 'Tet switch hooi; Gil, transmitter G7, closed contact 73, line limb l?, normal contact 72 of the cut-oill relay CO, norinalkcontact 77, and the Winding or relay LR to the grounded pole ofthe battery B. The resulting movement of the contact 77 to its alternate position closes nevv energizing circuit for the line relay Llei, which may be traced from the live pole of battery B", through the Winding of relay ot the master-switch G, closed contact 7S of the cut-od relay C0, and alternate contact 77 of the line relay, through the Winding of said relay to ground. The closing of this circuit continues the energization of the line relay and actuates relay'Q-l so as to close its contact 79 to complete a starting circuit :tor one of the line selectors Q, as Will be hereinafter explained. The movement of the Contact 8O of the line relay LR removes the normal ground connection from the contacts 80, 30', corresponding to the calling line, this ground connection `normally existing through normal contact Si of the cut-'oil' relay C@ and normal contact SO of' the line relay LR.V ln addition to the removal of this ground, which establishes that condition which will cause the line selector Wipers to step in engagement With the contacts of the line alter they have been movedto the desired group, the

season actuated contact 80 closes an energizing circuit -or relay 82 which in turn opens its contact 83 to remove the normal ground from contacts B3, 33', which correspond to the group of contacts in which those of the calling line are located, thereby establishing that condition Whichwill cause the line selector to stop its primary movement at the proper group of bank contacts.y Normally, contacts 36, 36 are connected to battery through the Winding of the cut-ofi1 relay CO. rlhis is the `electrical condition of the test contact which corresponds to the idle condition of the line. lf the line is an Vindividual line, that is, the only one going to a substation. or is the last one of a group of lines going to a substation, its circuit connections are those produced by the manual switches 83', 84 when in the positions illustrated at the left in Fig. l. This arrangement places the contacts 36, 36 on open circuit ivhen the line is busy. When the `line is one or' a group going to a substation other `than the last, its circuit connections kare those produced by placing the manual switches S3', Sd in their alternate positions, as illustrated at the right of l by the circuit of line S P'. l/Vith this arrangement, contacts 36, 36 are grounded to establish the busy condition of the line. As far as the line running from substation M is concerned, it may be either, but for the purpose of simplifying the description, it may be assumed to be an individual line having circuit connections produced by the manual switches 83', 8d when in the positions illustrated. lilith this assumption then, the shifting of contact Se oit relay LR Will interrupt the normal battery connection of contacts 36, 8G and Will replace such connection by an open circuit.

The master-switch Wipers 20, 2l are brought, attereach operation of the line selector Q, into engagement with contacts 22, 23, assigned to an idle line selector, as will be hereinafter explained. Thus, as soon as relay 2d isl energized, a starting circuit for such line yselec-tor is completed by a connection 'from battery B', through the Winding of primary relay PR, oil-normal contact 85, contact 22, Wiper 20, closed contact T9, and normal contact Soto ground, thus operating relay PR to complete a circuit from the live pole of the alternating or pulsating current generator 87, through the Winding vof the primary magnet PM, and alternate contact 88 of primary relay PR to ground, thus causing the Wipers 26, 27, 2S and 29 to move in a primary direction. The said group relay 82 has-its Winding connected to a plurality ot' alternate contacts 80, as indicated by the symbol shovvn (which sign serves throughout the drawing to indicate a common connecting point) on as many dillerent line relays LR. Thus in the example chosen, there would be one hundred line relays and ten group relays for a group of one hundred calling lines. Each group relay would then be connected to ten diierent line relays. Each of the ten bank contacts 33 therefore corresponds to a different sub-group of ten calling lines. Since the primary oH-normal contacts PO are actuated upon the first primary movement of the switch wipers, the initial energizing circuit of the primary relay PR is interrupted, hut in the meantime the closing of contact S9 of said relay has completed a new path through wiper 29 which is maintained as long as said wiper engages grounded contacts 33. The end of the wiper 29 is preferably made broad enough to bridge adjacent contacts so that it will not pass out of engagement with one contact before engaging the neXt, thus insuring a circuit at all times except when an ungrounded Contact 33 is engaged. It should also be noted that although the wiper 29 is normally out of engagement with contact 33, it engages said contact at the time the primary off-normal contact 85 breaks, thus insuring a suitable circuit for the relay PR until the wipers have been moved to that group of banlr contacts which includes the contacts assigned to the calling line. Just as soon as this group of contacts is reached, the primary movement of the switch wipers will-be discontinued, and the contacts 8S, 89 of the relay PR will return to normal. The return of contact 88 will immediately energize the secondary relay SR over a circuit extending from the live pole of battery B', through the winding of said relay, secondary off-normal contact 90, primary ottnormal Contact 91, normal contact 88 to ground. The movement of contact 92 of relay SR to its alternate position will at once close an energizing circuit for the sccondary magnet SM extending from the live pole of the alternating or pulsating current generator 93, through the winding of the secondary magnet, alternate contact and normal contact 9st of release relay RR, to ground. The resulting repeated energizations and denergizaticns of the secondary magnet will cause the wipers Q6, 27, 2S to move in a secondary direction over contacts 30, 31, 32, respectivelyv` of that group of bank contacts including the contacts of the calling line. Since,y upon the first secondary movement, the contacts of the secondary olf-- normal switch S() are actuated, the initial energizing circuit of the relay SB will bc interrupted.y but in the meantime the closing f its contact will provide a new path through normal contact 96 of release magnet RM to wiper 26 and thence to ground so lon as said wiper engages a grounded con tact130. 1t will be noted in thisV case, as ink the case of wiper V29, that the end of the Wiper is preferably made broad enough to bridge the space between contiguous contacts, and that although normally out of engagement with the nearest bank contact, it will engage said contact by the time the secondary off-normal contacts yare moved from normal. Thus ythe secondary movement of the switch wipers will continue until wiper 26 engages an ungrounded contact. Since the contact 30, corresponding to the calling line, has been ungrounded as previously pointed out, the wipers will be stepped into engagement with the contacts corresponding to said line. Since other subscribers lines are multiply connected to contacts over which the wipers 27, 28 pass during this secondary movement, and since conversation may be going on over a connection including said contacts, the relay SR is arranged to electrically disconnect the wipers 27, 28 from other parts during this secondary movement. This is brought about by the contacts 96, 97, which in their normal positions join the adjacent portions of the strands L, L', but, when actuated, separate them, thus disconnecting the said wipers. Thus as soon as the wiper 26 engages an ungrounded contact 30, the relay SR is denergized and the contacts 92, 95, 96, 97 return to their normal positions, thereby disconnecting the further secondary movement of the wipers and restoring the normal connections of the wipers 27, 28. The contacts 96, 97, when in their alternate positions, connect the right-hand portions of the strands L, L by a bridge which includes alternate Contact 96, closed contact 9S of release relay RR, and alternate contact 97. rIhe same portions ofthe strands L, L are united by a bridge including normal contacts 99, 100 of reversing relay RV, windings or" primary and secondary relays PR and SR and batteries Y), b. These batteries, being arranged in series, supply currrent over a circuit'including both of these bridges and thereby energize relaysk PR and SR to actuate their contacts. This prevents the possible closing of the release circuit (when the secondary off-normal contacts SO are actuated) from battery B, through the winding of release relay RR, closed contact 101, contacts 102, 103 of relays PR and SR', and the winding of release relay RR of the first selector U t ground.l

The restoration of the Contact 92 to normal. since the contact 104 of the secondary (iE-normal switch SO is now closed, immediately completes a circuit which is instrumental in causing the movement of the master-switch O to engage contacts of an idle line selector. This circuit extends from ground at contact 94: of release relay RR,

through said normal contact 92, closed con tact 104, Contact 23 and wiper 21 of the lac Y the circuit or master-switch, and Winding of relay 25 to the live pole ot the battery B, thus energia ing said relay to move its contact 86 to its alternate position and thereby close an energizing circuit for the motor magnetiltllvl, which includes theY alternating, or pulsating, current generator 105. Due to the mechanical relation ot the parts, the energization and ldeenergization of this magnet will step the Wipers 90, 2l into engagement with the next pair et banlr contacts. lf the line selector, corresponding to this pair, is in use, there exists a ground at one point or another, as Will be explained, on the corresponding'contact n3, which will maintain the relay 25 energized and thereby maintain the motor magnet. As soon, however, as an ungrounded contact 23 is encountered, this energizing circuit for relay 25 vvill be interrupted. Contacts 23, corres aonding to busy line selectors, will al- Ways be grounded, while those corresponding to idle line selectors will be ungrounded, thus securing the stopping of the mastersWitch with its wipers in engagement with contacts corresponding'to an idle line selector.v The ground connection with the contact 93 may exist over the path inst traced through contacts 10e, 92, 9st, or by Way of alternate contact 96, alternate contact 95, closed contact 90, closed contact 91, and alternate Contact 8S to ground. Or the said ground may be obtained through the oili'iormal contact 1262 ot the primary oft normal switch FO of the rst selector or at other times through the closed Contact 195 et the reversing relay RV and closed contact 174 of the relay a5. Y

As soon as the secondary relay SR of the line selector has been denergized and the adjacent portions ot the strand L, L united, circuits are at once established for the primary and secondaryV relays PR and SR Vin Vlieu of that circuitpreviously traced through alternate contacts 90', 97 of relay SR, Thus a circuit extends from the live, or negative, pole ol the battery B, through the Winding ot cut-off relay CO, contact 1062-107 of said relay, banlr Contact Si, vviper 97, strand L, normal Contact 99 of reversing relay RV, Winding ot the primary relay IPR, to the live, or positive, pole ot the grounded battery b. At the same time, a circuit is completed from the live, or negative, pole of the battery b', through the Winding oi secondary relay SR', normal contact 100 of the reversing relay RV, strand L including contact 97, vviper Q8, contact 32, normal Contact T6, and coil 7l to the negative pole of "battery B, prior to the operation of the out-oid2 relay CO; and irnniediately subsequent thereto, over linelimb S, contact T5, Vlock-magnet T4, switch-hook 6e, transmitter 67, contact 7o, line limb P, alternate contact T2 et cut-oil relay CO,

contact 3l, Wi per Q7, link strand L including contact 96', normal contact 99 ot reversing relay RV, the Winding of primary relay PR, to the positive pole or" battery l). The closing `of these circuits maintains the relays Plt and SR energized and, in addition, energizes the cut-oil relay C@ and the lock controlling relay :7l of the calling line. The movement ot contact 72 ot the cut-oit relay to its alternate position continues line limb P to contacts 3l, Sl, and interrupts the initial energizing circuit or' the line relay LR and thus destroys the normal substation control oi said relay. rEhe opening et its contact TS likewise interrupts the circuit established through relay 2l. ot the master-switch and the line relay. The opening of contact T6 interrupts the normal connection of battery B to the line limb S closing a circuit through relay CK from battery at alternate contact 70, Contact 77, Winding of said relay GK to grounthenergizing said relay CK which locks itself through the upper contact thereof and also opens the contact TW. The opening ot the contact T2 prevents the relays C() and PR from locking up, in series through alternate contacts 10T and 72 and along the upper heavily marked conductors when alternate contact i' is closed. Thesubscribers circuit is thus completed over the heavily marked lines to the sections ot the strands L, L', lying beyond the condensers 108, 109. lThe movement ot' contact 8l interrupts the path for current over the strand L, through the cutoff relay CG, butbetore said circuit vis interrupted, a new circuit is provided tor the cuteotl7 relay, through contact lOl-Shengaged contact 30, Wiper 26, normal contacts 96 and 95 to ground. llhus the cut-oli1 relay CO is maintained energized. lilith the manual sivitches S3', Si in the position illus trat-ed, giving connections for individual lines and the last lines orp groups, the guard upon contacts 36, 36 is provided by opening the circuit of such contacts, first, at normal contact Set during the energization of relay LR, and later, at contacts 100 during the energization of ythe cut-oil3 relay CO. lilith the manual switches 83', Sal in their alternate position, giving the connections for the lines of a group other than the last, contacts 30, 36" are connected to` ground, first, at alternate contact Si during the energization et relay LR, and later. during energization of cut-eti' relay C0, via normal conv tact 84, manual switch Set', Contact 107-81, contact 30, Wiper 26, normal contacts 96 and 95, to ground. rlhe guard is placed upon contacts 30, 3l over this same path to ground, through alternate contacts 96, 95. The disconnection and consequent denergizationot line relay LR causes the release of the group relay 82 unless there is another line relay belonging to the saine sub-group llO of teu energized at this time for the purpose of also initiating a call. Assuming no such condition to exist, the release of relay/82 Will restore the ground via contact 83 to bank contacts 33, 33', etc., thereby permitting Wipers 29 of said other line selectors to rotate past the sub-group containing the calling line Whose call has been picked up Also, the denergization of the line relay LR causes that of the relay 24 of the mastersyvitch (D, unless there be at that time another line relay belonging to the same group of subscribers then initiating a call. Assuming there be no such other call existing, the release of such relay 24 Will prevent the starting of another line selector When the master-switch steps its Wipers 20, 21 around to engage the bank contacts corresponding to the next idle line selector. All of the operation thus far described results from the removal of the receiver at the calling station, and as We have seen, extends the subscribers line to a first selector U.

With the parts in this position, the calling party begins to operate his calling mechanism 68 to extend his circuit through to the called line. rlhe calling mechanism is diagrammatically represented by a disk having a Anumber of teeth adapted to'engage spring 73 to cause it to break Contact upon the return oi' the disk under the influence of its return spring 112, and a single tooth similarly coperating' With contact spring 75 to cause it to open its contact after the Contact 73 has completed its interruptions. The disk is also provided With a pin Which engages the spring contact 113 to hold it out of engagement With a similar spring contact 11i and a grounded contact Y115. The disk is normally locked by means of a hook 11G arranged to engage a notch in the disk and normally held in engaging position by a spring and moved out of engaging position by the energizations of the magnet 74. In operation, the disk is moved against the tension oi its return spring until a denite number of teeth have passed below the spring 73, and it is then allowedto return to normal with the resulting breaking of contacts 73 and 75. Under the assumption that the number of the called station N is 8450, the calling party Will rotate his dial tar enough to bring three teeth below the contact 73 and will then release the same to allen' it to return to its normal position, and he ivill follow this operation by similar operations in Which he Will rotate the dial sufliciently to bring, next, four teeth, then tive teeth, and finally six teeth below the spring contact 73. Considering only the effect of the first operation, it Will be noted that as soon as the dial is removed from normal, contact 73 Will be grounded through con'- tacts 113, 114, 115; and While this ground remains, the primary relay -PR' Will be energized from the battery over the strand L, line limb P, through contact 73 to this ground at the substation, While secondary relay SR' will be energized from battery Zi', over the strand L', line limb S, and contact 75 to the same ground. Consequently, the three resulting breaks and makes of the contact 73 Will cause three deenergizations of the primary relay PR', and the single following break and make of the the contact 7 5 Will cause a single denergr yzation of the secondary relay SR. An inspection of the contacts 121, 122, 123, 12a of the primary and secondary relays PR', SR' Will shov that the three denergizations of the primary relay PR' will cause the section of the strand L to the right of condenser 108 to be grounded three times, While the single denergization of the secondary relay SR' vvill cause the section of the strand L' to the right of the condenser 109 to be grounded once. lVhile relays PR' and SR' are energized, these sections of the strands are not grounded by reason of the open contact 122 in one case, and the open contact 12a in the other. From this it Will be seen that the passage ot each tooth past the contact 73 has the effect of producing a momentary ground upon the section of strand L to the right of condenser 108, and that each movement of the single tooth past contact 75 has the effect of producing a single momentary ground upon the section of the strand L' to the right of condenser 109. Thus the grounding of the strand L three times has the effect of producing three dis-V tinct energizatins of the primary magnet PM' of the first selector U, the circuit being from the live pole of the battery B2, through the Winding of said magnet, closed contact 125 of the secondary oli-normal switch S0', and strand L to ground. These three energizations ivill cause the Wipers 39, 40, 41 to move to the third group of bank contacts 42, 43, da. Upon the rst movement in this direction, the primary orinormal contacts PO will be closed. Consequently, upon the subsequent grounding of strand L', secondary relay S'R Will be energized over a circuit extending from the live pole ot the battery B2, through the Winding of said relay, closed primary oii` normal contact 126, closed secondary ott-normal contact 127, and strand L' to ground. The energization of relay S'R' Will open its contacts 128, 129 to disconnect the Wipers a0, a1 to prevent interference with possi-v ble conversationV over multiply connected bank contacts in the manner heretofore pointed out in describing the line selector. The closing' of contact 130 of relay S'R' Will energize secondary magnet SM' by closing a circuit extending from the live pole of alternating or pulsating current generator normal contact 132 of release relay RR, and closed contact 130 ci relay Sli to ground. Bue to the mechanical relation of the parts, the repeated. energizations and deenergizations et the secondary magnet Will cause the Wipers to more in their secondary magnet will cause the Wipers to more in their secondary direction- Upon their iirst step in this direction, secondary oli-normal contacts SG Will be opened, thus interrupting previous circuits for the primary magnet 13M and the second ry magnet SR. ln the meantime, the increment of contact to its alternate position proyides a substitute energizing circuit. 'for relay SR Whi ch entends ria said Contact, normal contact 13a'. of release relay RR', and closed contact of release magnet liti to Wiper 39 and thence to ground as long as said Wiper engages grounded contacts i2. ln this case, as in the case oi' Wipers 26 and 29, the end of the wiper is made sufficiently broad to engage a neu' contact betere disengaging a previous one. ln case the encountered con tact is that of a busy second selector V, its ground connection Will extend over a Wiper ot another iirst selector, through its closed contact 135 and normal contacts 1.3i `rilhis secondary movement of the selector Will continue until an ungrounded contact i2 is encountered, whereupon the selector Will stop. As soon as this happens, relay S R Will be de'e'nergized, With resulting connection ot the Wipers fil), 11 to the strands L, L", a resulting interruption ot the secondary magnet circuit and the restoration ot ground to the Wiper and to multiply connected bank contacts d2, thus rendering the selected second selector busy to other seeking iirst selectors. Thus, by this operation ot the calling mechanism, the circuit ot the calling line is extended over the heavily marked path to a second selector oi2 the third. thousand group.

lThe next step in the operation consists ink operating the calling device to iirst ground the strand L tour times and then to follow with a single grounding of the strand L through the agency ot the primary and secondary relays Pit and SR, as heretofore. The operation of the second selector in response to Vthese impulses is substantially the same as that oi: the first selector just described. The grounding of the strand L four times causes tour distinct energizations ot the primary magnet Plv 2 to cause the Wipers L16, a7, 48 to advance to the fourth group of bank contacts 49, 50, 51, and the singley groundingV ct the strand L through the agency ot the secondary relay Sitzy and secondary magnet SM2 starts the Wipers over the contacts in this group of bank contacts, and this secondary moyement of the Wipers is continued until an idle contact is encountered, The circuit of the primary ness-anos magnetvextends from the live pole. of the battery B2, through the Winding of said magnet, secondary onf-normal contact 136, contacts 113, a0, 12S, strand L to ground yia contacts 122,123. The initial energizing circuit Jfor the secondary relay SR2 extends Jfrom the liye pole of the battery B2, through the Winding ,oisaid relay, closed primary ofi-normal contact 137 (closed upon the first primary movement ot the switch) and closed secondary oit-normal contact 138, contacts est, 411, 129, strand L to ground via contacts 12a, 121. ri maintaining circuit is then established tor the relay by way of the closed contact 139, closed contact 140 ot release magnet RN?, to Wiper 16 and contact 49 to ground, as long as grounded contacts are encountered, The ground connection, as in the case of the first selector, is obtained by Way ot a multiple contact i9, Wiper 46 of some other second selector V engaging said contact, closed contact 140, and normal contacts 141, 142 of said other second selector. rllhe circuit ot the secondary magnet similarlyT runs from the live pole of an alternating or .pulsating current generator 1118, through the Winding of said magnet, normal contact 144C of release relay lili-2 and alternate contact 1412 to ground. rlhe Wipers el", 1S are also disconnected during the secondary movement by contacts 1&5, 1&6 of the secondary relay SR2. r1`hus, as a result of the transmission of the tour impulses, the circuit ci the calling line is eX- tended to a connector having access to the fourth hundred group of the third thousand subscribers lines.

The nent step in' the operation consists in grounding the `strand L frye times, followed by a single grounding of the strand lj, through the agency et the primary and secondary relays PR" and SB as before. rilhe grounding of the strand L ye times causes five distinct energizations ot the primary magnet Pll/lrwhich, due to the mechanical construction of the parts, causes the connector Wipers 52, `53, 511 to be moved to the nfth group of bank contacts including contacts 55, 56, 57. lThe energizing circuit for the primary magnet extends from the live pole et the battery B3, through the Winding of said magnet, contact 1&7 of the secondary cti-normal switch S03, contacts 50, 17, closed contact 1415, contacts 43, d0, closed contact 128, and strand L to ground. @n the rst` primary movement, as usual, the rprimary ott-normal contacts P03 'are closed, and consequently upon the single( grounding of the strand L', a circuit is completed through the Winding of the secondary magnet Sli/i3, which may be traced from the live pole of battery B3, through the Winding of said magnet, closed contact 1%8 of the primary onormal switch i303, contact 14:9 of the secondary oli-normal switch S03, contacts 51, 48, closed contact 146, contacts 44, 41, closed contact 129, and strand L to ground. In the construction of the connector, the wipers are located two steps distant from the first set of bank contacts, and the resulting single momentary' energization of secondary magnet SM3 is instrumental in stepping these wipers one step nearer the said bank contacts; and, due to the spacing of the contacts of the secondary off-normal switch S03, this first secondary step of the wipers causes Contact 147 of olf-normal switch S03 to move to its alternate position and causes contact 149 of said switch to move out of engagement with its normal contact, but not into engagement with its alternate contact, the later movement being performed by the next secondary step of the wipers.

The next step in the operation consists in grounding the strand L six times, followed by a single grounding of the strand L. Due to the position of the contact 147, the grounding of the strand L six times causes six distinct energizations of the secondary magnet SM3 over a circuit extending from the live pole of the battery B3, through the winding of said magnet, closed contact 150 of relay R, alternate contact 147, contacts 50, 47, and so on over the heavily marked path to ground at strand L. The first energization of theV secondary magnet SM3 steps the wipers into engagement with the first set of bank contacts in the desired group and moves contact 149 to its alternate position. The six distinct energizations, therefore, move the wipers into engagement with the sixth set of bank contacts in the particular selected group, and these, under the assumptions made, are the contacts 55, 56, 57, the contacts of the first line running to substation N. Thus a complete connection is established from the substation M, over the heavily marked circuit, to the substation N, except that the strands L2, L3 are interrupted at the relay CR, which I may term a closing relay. The further action of the apparatus depends upon the electrical condition of the test contact 55 encountered by the wiper 52. These dierenty conditions may now be considered.

Fir/st called Zine idle.

It will be noted that the above connection is completed without the application of the final ground to the strand L. When this is applied, a circuit is completed through the lower winding of the relay RG, which, for convenience, I may term a ringing7 relay because part of its function is to control the application of ringing current to the called line. The energizing circuit for this relay extends from the live pole of the battery through the lower winding 151 of said relay, closed Contact 152 of busy relay BR, normal contact 153 of relay R, strand L3, alternate contact 149, contacts 51, 4S, and thence over the lower heavily markedy path to strand L and ground. The energization of relay RG, resulting from the closing of this circuit, is momentary only. Under the assumption that the first line of the group running to substation il, which line has contacts 55, 56, 57, is idle, contact 55 will be connected to battery B3 by a path extending from the live pole of battery B3, through cut-off relay CO of that line, manual switch 84', normal contact 84, to contact 55. The momentary energization of relay RG completes al circuit through the lower winding 154 of busy relay BR, which may be traced from the live pole of the battery B3, through protective resistance 155, winding 154, closed Contact 156 of relay RG, and normal contact 157 of relay R, to ground. Accordingly, relay BR is energized and thereby immediately completes a circuit through its closed contact 158 and the upper winding 159 of relay RG. Its energization also breaks the initial energizing circuit for relay RG at contact 152. In order to insure the closing of the circuit through the upper winding of relay RG before that through its lower winding is broken, contact 152 should be adjusted so as to break after or substantially at the same instant that contact 15S is made. rIhe energization of relay BR also closes a circuit for relay R through its contact 160, to ground, thereby energizing the said relay R to interrupt the circuit through the lower winding 154 of relay BR at contact 157. Under the assumed condition of encountered contact 55, relay BR thereupon drops back and interrupts the circuit of winding 159 of -relay RG and allows that relay to return to normal also. The relay R, however, remains energized, locking itself up through its contact 161 and contact 162 of release relay RR. The initial energizing circuit for relay RG is also interrupted at contact 153 upon the energization of relay R; and at the same time, the connection of secondary magnet SM3 to the primary side of the circuit is broken at contact 150. From this description, it will be seen that when battery is connected to the test contact 55 of the called line, relays RG and BR operate and then return to normal and relay R operates and is locked up. In the operation of relays RG and BR, relay RG is the first to attract its armature and the last to retract its armature. This relation in the operation of relays RG and BR prevents the improper operation of the circuits by which the switch is stepped ahead automatically and by which the busy back signal is transmitted to the calling party and obviates careful adjustment of these relays. As soon nate contact 107, normal Contact f7 2',

ground.

as relay BR returns to its normal position after ythis preliminary operation, a circuit is completed to operate the secondary ringing relay BG. This circuit extends from battery, through cut-oil3 relay C@ to the test contact 55, and thence through Wiper 52, contact 163 of relay BG', normal contact 164 of relay BB, closed contact 165 of relay B, normal contact. 166 ot relay BG, and the Winding of said relay to ground. Relays C() and BG are thereupon actuated; relay CO locking itself up via altercontact 56, Wiper 53, impedance coil 182 and closed contact 1830i relay BG to ground, and relay BG locking itself up through'its alternate contact 166, normal Contact 187 of release relay BRS, the closed primary oiinorinal contact'168, protective resistance 169 to the lire pole of battery B3. Tn this operation, contact 183 ot' relay RG makes before contact v163 breaks. By closing its contact `170, relay BG completes a circuit itroint-he liye pole ot battery B3, through protectire resistance 171, normal contact 172 otA tip relay TR, closed contact 170 and the upper Winding 159 of relay RG to ground, thereby en rgizing krelay 'BG to close its contact 173 to completea circuit for the flip-flop relay FF. This circuit extends from the live pole ot the battery B3, through the flip-nop relay FF, normal contact 174, closed contact 173, and closed contact 17 5 through interruptor 176 to At this time, tip relay TB has its Winding connected to the back contact 177 of flip-flop relay FF, through contact 178 ot relay BG', contact 17 9 ot' relay RG, and contact 180 ot relay BR. The iront contact 177 ot relay FF is connected to a suitable ringing source such as the grounded alternating or pulsating current generator 181.` By the operation of the iiipflop relay, the tip relay TB., and the generator 181 are alternately connected to the tip side ot the circuit. During the ringing interyal, current Hows out over the line, through the condenser and call-bell at the substation, and bach to ground at the cen tral station through impedance coil 182 and'grounded contact 183 of relay BG. During the noneringing interval, the geir erator tap is replaced by a tap through the tip relay TR', as just traced. The circuit by which relay BG Was actuated also actuated cut-oii relay C0 o1" the called line, since the battery connection to contact included the Winding oi said latter relay. Since the busy condition ot the line, having the contacts 55, 5G, 57, is that in 'which a ground is placed upon Contact 55, ground connection must be found running to said contact as soon as the Wiper 52 `engages contact This ground connection eX- ltendsviirom contact through normal contact 81 of line relay LR, manual Yswitch 81', alternate contact 107, normal contact 72', bank contact 5G, Wiperr, impedance coil 182 and closed contact 183 to ground. As soon as the called party responds to the signal ot his call-bell by removing hisy receirer from its hook, a conductive path is completed between the limbs oit his line; and as soon as the nip-liep relay is brought into its nonringing position, the tip relay TR is energized over a circuit whichV also constitutes the circuit for supplying transmission current. to the transmitter at they called substation. This circuit extends from the liye pole of the battery B3, through protective resistance 171, tip relay TR, closed contacts178, 179, 180, normal contact 177, to one side of the lcircuit, thence out oyer the line, through the called station, back over the line, returning to the opposite pole ot the battery through impedance coil 182 and closed contact 183 ot relay RG. The actuation ot' tip relay TR interrupts the circuit through the upper Winding 159v ot relay BG, by opening its contact V172. By closing its contact 18st, relay TR causes the energization ot closing relay CB., which immediately locks up through its contact 185 and contact 162 ot release relay RRS. The denergization of ringing relay BG interrupts the circuit ot Hip-flop relay. FF' and also interrupts the connection from the tip relay to the sleeve side of the circuit previously traced. Before this latter connection is broken, however, a substitute path is pro vided from said relay TB., through its contact 186, contact 180 of relay BB, and normal contact 177 of relay 11F to the saine side ot' the circuit. tact 187 of relay TR prevents the closing ot' a release circuit through relay BB3 upon the subsequent operation ot closing relay Clt, this circuit extending through protectiye resistance 171, contacts 187, 188, and the VWinding of relay Bll-fto ground. The operation of relay CB- opens contact 189 to disconnect the'busy bach device BB; and by the operation of said contact 189 and contact 190,the talking strands L2, L3, are completed so as to complete the conversational circuit between the substations M and N. Contact 17% of this relay also interrupts the circuit of dip-flop relay FF. `lontact 190a places a ground upon the bank contact 119 ot the associated second selector as a guarding potential.` While relay GB remains denergized, this path extends Jfrom contact 19, through contact 191 of the primary ofinorinal switch P03, normal contact 1902 and Winding of release relay BB3 to ground. seen, contact 1880i this relay closes a normally open point in the release circuit of releasel relay BB3.

The yopening' of conf ris We have From the previous description, it will be seen that as soon as the called party has responded to the call and the tip relay has been operated, there will be atlow of current through the relay 45 associated with the reversing relay RV, which may be traced from battery B2, through the winding of relay 45, alternate contact 1211 of relay SR, strand L', over the lower heavily marked circuit to strand L3, thence through closed contact 190 of relay CR, impedance coil 182 and closed contact 183 of relay RG', to ground. The opening of contact 192 of relay 45 will prevent a possible release circuit through release relay RR when the reversing relay RV is energized. As is clear from the cross connections 193, 1911-, the energization of relay RV disconnects primary relay PR from strand L and connects it to strand L, and similarly disconnects relay Slt from strand L and connects it to strand L. Thus the supply of current from batteries b, 5 to the sub-station M is reversed. This reversal of current is for the purpose of operating any of the well-known devices such as paystation and meter devices, which are commonly employed in systems of this class. as pointed out heretofore, the ground connection with the contact 23 of the master-switch O is obtained through a contact 195 of the reversing relay RV.

During conversation, current for transmission is supplied to the calling party from the batteries and to the called party from the battery B3, over circuits which have been previously traced.

First called Zine busy.

N ow, if it be assumed that the tirst line running to substation N is busy, either because a call has been initiated over it, or because it has been connected with as a called line, then, as previously noted, it being the first line of the group, its test contact 55 will be connected'to ground. This ground connection may be over any one of several paths depending upon the state of operation. It may extend through alternate contact 8st and manual switch 83'; or through normalcontact 84:, manual switch 84k', alternate contact 107, and thence through bank Contact 30 to ground at contact 95; or through normal contact 8l, alternate contact 107', closed contact 72. contact 55, wiper 53, impedance coil 182, and closed contact 183, the latter giving a ground connection when the line is in use as a called line. lilith this ground connection upon test contact 55, the relays oi' the connector circuit will operate somewhat differently than before described. The iinal secondary impulse, transmitted to the connector, will, as before, result in momentarily energizing relay RG with a consequent inomentary energization of relay BB, but this latter relay will not be allowed to return to normal as in the previous case, but will be held up by current over a circuit extending from the live pole of the battery Bi', through the lower winding 151 of relay RG, the upper Winding 195 of relay BR, alternate contact 164; of said relay, normal contact 163 ot relay RG', wiper 52 and test contact 55, to ground. It will be noted that this circuit includes the lower winding of relay RG, but the contacts of said relay are allowed to return to normal under the differential action of the winding 159, which was brought into circuit upon the closure of contact 158 of relay BR, as before explained. Thus, under this condition, relay BR maintains its contacts in their attracted position, while the contacts of relay RG return to normal. rllhe eili'ect of this action of the relays is to close a circuit which will cause connector' W to advance one step. This circuit may be traced from the live pole ot the battery B3, through secondary magnet Sli/13, its vibratory contacts, normal contact 197 of relay RG, and closed contact 160 of relay BR to ground. Because of the relation of the inechanical parts of the switch, the actuation of relay SM3 will step the wipers 52, 53, 5-1 into engagement with contacts 55a, 56a, 57a, corresponding to the second line running to substation N. lf this line be found busyin other words, it it be found with its test contact 55EL grounded-then the relay BR will be maintained in its attracted position, and the secondary magnet SM3 will cause an additional step of the switch. It' the second line, namely, that having the test contact 55a, is idle, said contact will be connected to battery and the further advance of the switchwill be prevented and relay BR will return its contacts to normal and ringing current will be applied to the called line in the manner heretofore explained in connection with the first line running to substation Upon reference to the circuits, it will be noted that when connector switch il] is operated to connect with the line terminals 55, 56, 57 of a. busy line, any one ot several conditions may exist upon test contact 55, depending upon whether the line be busy as a called or calling line. For instance, if the line be ak calling line, its test Contact 55 will be connected to ground over a circuit, extending to the ground at normal contact 95 of a line selector Q. Second, if the line be a calling line, until said line is picked up by a line selector, the ground connection to its test contact 55 will extend from the ground through switch 83 during the time the line relay is energized. Third,

if the line be busy as a called line and the called lsubscriber has not yet removed his receiver from its switch hook, the test contact 55 will be connected through impedance coil 182 of the connector switch to ground at the closed contact 183. nother ciruiit will extend trom the test contact through the cut-oli relay C() to the live pole ot' battery Bf". Fourth. it the line be busy as a called line, and sulirscriber has responded to the call, a` circuit will extend from test contact through the impedance coil 182 to ground, a second circuit trom said test contact through the cutoii' relay CU to the live pole ot battery B1", and a third circuit will entend from this test contact normal contacti, closed contact 107, closed contact TL out over the called line, returning over contact 57, Wiper 5%, and through test relay TR to the live pole of battery B3. fdo it will be seen that when iviper engages 'the test contact oit a busy line, any one of said tour conditions may be encountered, and therefore the ditierential relay RG and the Winding or' the relays, resistances or impedance coil which have to do With any of these tour conditions are to be so related that the ditlerential relay RG will retract its armature upon its test Wiper engaging the iirst test Contact 55, it connected under any ot the tour conditions described, and maintains its armature retracted While the Wiper is engaging `test contacts connected under any of the said conditions.y in practice l have found that with a battery strength oi' 50 volts and With the following resistances, the system Will operate satisfactorily although it is to be understood that l do not Wish to be limited to thse resistances of voltage as others suitable may be used; relay TR, 200 ohms; relay RG, 100 ohms in each Winding; relay BR 100 ohms in each Winding; cut-ott relay CO, 1000 ohms; protective resistance 155, 300 ohms; impedance coil 182, 200 ohms; resista-nce connected to sivitch 831, 200 ohms; and the resistance connected between ground and normal contact of line switch Q00 ohms.

Last called Zinc busy.

From the description oit the operation thus far given, it is clear what Will happen it the iirst tvvo lines of the group of three running to substation ll are idle, or busy. NOW, if it be assumed that the first tivo lines-those having test contacts 55, 55- are busy, and that therefore the connector has been automatically stepped so as to bring its Wipers 58, 5% into engagement With contacts 55h, 56D, 57h, namely, those of the last line et the group running to substation N, then the operation will be the same as in the case of either ot the preceding lines,if said last line is idle; but it said line be busy, then the operation is diiterent than heretofore described. in the latter event, it will be remembered, test Contact 55D is on open circuit. lt has connection neither with ground nor battery. As betore, the final secondary impulse transmitted over the line from the calling station to the connector will momentarily energize relays RG and BR. rlhc return otl the contacts ot both oi' these relays to their normal positions Will be instrumental in closing a circuit from the busy back device BB, so as to indicate to the calling party that all the lines ruiming to substation hl are in use. The primary portion or' the busy back circuit eX- tends from the live pole of the grounded interruptor 198, through the primary winding or' the induction coil 199, through the various battery connections to ground. The secondary portion oit this circuit extends from the live pole ot said battery, through the secondary Winding or induction coil 199, the condenser 200, the oli-normal contact 201 (here designated as a primary ott'- normal contact, although a secondary ott"- normal contact may be employed for this purpose), closed contact 202 oii relay RG, closed Contact 203 ot relay BR, normal contact 189 of relay Citt, to the strand L2 and `thence over the heavily marked circuit through the calling substation M, and baclt over the opposite side of the circuit to the ground, between batteries l), 7o', or elsewhere, on that side otl the circuit.

llrom this description, We have seen that the relays RG and BB assume diierent relative positional conditions, according to the different electrical conditions of the encountered test contact 55, or b, and that in accordance with the condition of these relays, ringing current is applied to the called line, the connector is automatically advanced, or the busy back signal is transmitted to the calling party.

Release.

The manner of releasing thev various switches employed in establishing' either a portion otl a connection or a complete connection may new be considered. Assuming that the connection has been completed betiveen substations M and N, and conversation has been carried on 'between these sta.- tions, it' the calling party at substation M nrst hangs up his receiver, all the switches will be released and restored to normal eX- cept the connector lV; it then, the called party at station N hangs up his receiver, this connector too Will be released. lf, on the other hand, the called party tiret hangs up his receiver, then the first selector U, second selector V, and connector TV ivillbe released; and then, as soon as the calling party restores his receiver, the line selector Q will be released. Again, it it be assumed that the line circuit of a calling line has been extended through to the desired called line and the latter is 'found to be busy, then it the calling `party restores his receiver to its hook, all the switches Will be released and restored to normal. Likewise, if at any time in the process of extending the calling subscribers circuit, he decides not to complete thc call, he may restore his receiver to its hoolr. and thereby release all the switchesy which have thus far been operated, and they will be restored to normal.

Considering these releasing operations more in detail, it will be remembered that, during conversation, the relays PR and SR are maintained continuously energized over the calling line circuit. lThe restoration ot the calling partys receiver to its hook interrupts this energizing circuit and these relays become de'energized, thereby allowing their contacts 102, 103 to close, thus completing a release circuit which may be traced from the live pole of the battery B, through the lower winding of release relay RR, closed contact 101 of ott-normal switch SO, closed contacts 102, 103 of said relays PR and SR, and the winding of release relay RR of the first selector U to ground. The closing ot this circuit energizes both release relays RR and RR; the former, by closing its contact 204, completes a locking circuit extending through its upper winding', closed contact 91 of the primary oft-normal switch, and normal contact S8 of primary relay PR, to ground. This connection to ground from contact 204 also causes the energization of release magnet RM, which, due to the mechanical construction of the parts, releases the switch wipers and other parts and allows them to return to normal under the action of returning springs, as will be more fully explained hereinafter. In order that the wipers 27 and 28 may be disconnected from other parts while returning over the banlr contacts 31 and 32, thereby preventing interference with conversation through multiply connected contacts, the relay SR is energized during this return movement. The energizing circuit for this relay extends from the live pole of the battery B, through the winding of said relay, alternate contact 90 of secondary ott-normal switch SO, and alternate contact 94 of release relay RR, to ground. The locking circuit of the release relay RR is maintained until the primary oit-normal contact 91 is opened upon the return of the switch to normal. The energizing circuit of relay SR is also maintained until the wipers have completed their return movement in a secondary direction. At this time, the circuit is interrupted at contact 90 of the secondary oft-normal switch SG. Alternate contact 96 of the release magnet RM is instrumenta-l in placing a ground upon the associated master-switch bank contact 23 to cause the operation of the master-switch in case the release relay RR and release magnet RM are energized upon the liuc selector' selecting the callingline.l which. would occur the calling party hung up his receiver before the line selector had completed the selection.

The energization of release relay RR of the iirst selector U, by closing its contact 205, completes a circuit from the live pole of battery R2, through the winding of relay SR, closed contact 126, of the primary off-normal switch PO, closed contact 205 and the winding of relay RR to ground, thereby maintaining the release relay RR energized and energizing the secondary relay SR. The energizing of these relays closed a circuit for the release magnet Ri/l which extends from the live pole of the battery B2, through the winding of said magnet, alternate contact 132 and closed contact 130, to ground. The structure of the parts is such that the energization of this magnet releases the switch and allows its parts to return to normal. The energization or' relay SR also disconnects wipers 40, 41 during their return movement so as to prevent interference with existing' conversation over multiple connections. The circuit for the relays RR and SR is interrupted by the primary off-normal contact 126 when the switch has reached its normal position. The release of the Erst selector U is relayed to the second selector V by the closing of alternate contact 134 of release relay RR', over a circuit which extends from the live pole of batterykBg, through protective resist-ance 206, alternate contact 134, closed contact 135, wiper 39, banl contact 42, closed contact 207 of the primary ott-normal switch P02, and winding of release relayy RR2 to ground. This circuit is momentary only, being interrupted by contact 135 upon the energization of release magnet RM, but is of suicient duration to allow relay RR2 to lock itself up. This locking circuit extends from the live pole of battery B2, through the winding of relay SR2, olf-normal contact 137, closed contact 208, and the winding of relay RRQ to ground, thereby continuing the energization of the secondary relay SR2 and the release relay RRZ, as in the case of the first selector U. As in such case also, the joint energization of these relays closes an energizing circuit for release magnet RMP', which may be traced from the live pole of battery B2, through the winding of magnet RM?, and alternate contacts 144 and 142 to ground. The energization of the release magnet, as before, causes the restoration of the switch parts to normal; and during this return increment, the energization of secondary relay SR2 maintains the wipers disconnected to prevent. interference with conversation over multiple connections. Upon the return of the switch parts to normal, the contacts of the primary oit-normal switch P02 are opened, and thepreviously traced circuit of relays SR2 and; RRZ is interrupted.;

As before, the release of thek second selector V closes a circuit which may be traced from the live pole of battery 132, through protective resistance 209, alternate contact 1Ll1 of relay RRZ, closed contact 1el0 of release magnet Bldg, Wiper d16, banl; contact e9, closed contact 191 of off-normal switch 1303, and alternate contact 190All of relay to ground. Under the assumption that the calling party has first hung up .his receiver, the completion of this circuit does not cause the release of the connector lll. This release will not occur until the called party at substation N rest-ores his receiver to its hook. Thus it ivill be seen that if the calling party restores his receiver before the called party, switches Q, U and V Will be restored to normal. Non', When the called party hangs up his receiver', he -will interrupt the circuit over the line limbs by which the tip relay Tft was maintained energized, and at once a release circuit will be closed from the live pole of the battery B3, through protective resistance 171, norma-l contact 187, 'alternate contact 188, and the Winding of release relay lill@ to ground, thereby energizing said relay to close its alternate contact 162 and thereby energize release magnet Eli-i3, which, due to the mechanical construction of the. parts, releases the switch mechanism and allows it to return to normal. Since, during conversation, the relays B and CR are locked up over a Ycircuit including the normal contact 162, it Will be seen that these relays Will be de'ei'iergized upon the energization of release relay RRS. The energization of relay RRS by its contact 16? vfill open the loclring circuit of ringiiuY relay RG and alloiv it to return its contacts to normal. Since the cut-off relay CO is held up by current flowing through closed contact 183 of relay RG', it follows that when this latter rela-y is denergized, relay CO Will also be deenergized. Lilreivise, the return of the wipers 52, 53, 511 to normal will restore the primary and secondary off-normal contacts PGS and S03 to their normal positions. 1t may also be noted that the energization of relay Riti interrupts the locking circuit of closing relay CR so that said relay is deenergized, and upon its denergization it in turn opens the circuit ofrelease relay BB3, and thus all the parts are restored to Vnormal. NOW, if it be assumed that all the called-for lines are busy and that the calling party receives the busy signal, then the restoration of such partys receiver to its hook would cause the release of the switches U, V by the closing of the circuits in the manner just described; and furthermore, this act will restore the connector Tf. from the previous description, it will be reinembered that relay Gli not actuated until the called party responds to the call, if'

cordingly, the relayed action of the second selector V `svill not be impotent, as in the case just considered, but a circuit Will be completed upon the energization of release relay RR which, as before, Will extend from the live pole of the battery B2, through protective resistance 209, alternate contact 1&1, closed contact 140, Wiper 16, banlr contact e9, closed onormal contact 191, and thence, instead of direct to ground, through normal. contact 190L1 and the Winding of release relay Rit-3 to ground. Thus the release relay is energized With the consequent energization of the release magnet lll/13 and the restoration of the switch parts, as before described. To give time for this restoration, the release relay BH3 is loclred up over a circuit extending from the live pole of battery Bi, through protective resistance 169, closed olf-normal contact 168 and closed contact 167 of release relay RRQ', tok ground.

Now consider the case in which the called, instead of the calling, party first restores his receiver to its hook. ln such event, as heretofore, the circuit of the called line. is broken with the consequent deenergization of the tip relay TB- and the connector lll is released by the closing of its circuits in the manner heretofore described. it this point, it will be remembered that the reversing relay RV, by Which the substation v special devices are actuated by a reversal of is maintained energized duringl conversation by the continued energization of relay 45, Whose energizing circuit ei;- tends over one side of the heavily marlred circuit through impedance coil 182 to ground, as before traced. Consequently, when the called party restores his receiver to its hook, relay l5 is denergized. Thus a circuit for the release relay RR is'coinpleted. This circuit extends from the live pole of the battery B2, through protective resistance 210, closed Contact 192 of relay 45, closed contact 211 of relay RV, andV Winding of therelease relay RH to ground.V The energization of this relay is instrumental in causing the release of the first selector U With the subsequent release of the second selector V in the manner heretofore fully described. From this description, it will be seen'that if the called party first restores his receiver to its hook, all the switches employed in Vthe connection are restored to normal, except the line selector. This, however, is restored to normal as soon as the calling party interrupts his line circuit by restoring his receiver to its hool. This, as before explained, causes the closing` of contacts 1027 103 of the relays PR and SR', with the consequent energization of release relay RR of the line selector and the return of the parts of the line selector to normal.

1t remains ncrv to consider the effect of current,

lil() 

